Let’s discuss in some detail.
We will break down by part. Starter solenoid, factory fuel pump relay socket, and breaker VS fuse.
There are 4 posts on most Ford factory starter solenoids.
1) Big post #1 - Goes to the battery. Has other connections that need power from the battery, so Ford puts them here VS on the battery post connector. (You will likely do the same for your relay, more to come.)
2) Big post #2 - Goes to the starter.
3) Little post #1 - Goes to the truck wiring harness and gets power when you turn the key to start.
4) Little post #2 - When the starter solenoid is powered up by little post #1 and the inside contacts connect, little post #2 gets 12v positive power till the solenoid is unpowered seconds later after the vehicle starts.
When the solenoid is powered by little post #1 to temporarily to start the vehicle, it uses an electromagnetic force to makes two electrical connections inside contact each other. When this happens big post 1 and big post 2 are connected together and the starter turns. Also, when big post #2 gets power, little post #2 also gets power. (Not used on a diesel.)
So, for your first point - Using the starter solenoid for activation.
No one is hooking up the yellow wire (Relay activation wire) to the starter solenoid. That does not work with a standard relay. (Requires constant power to stay energized.)
a) If you hooked up the yellow wire (Diagram above.) to big post #1 (Battery power always.) the fuel pump would never turn off.
b) If you hooked up the yellow wire to big post #2, the fuel pump would only work when the starter was running.
c) If you hooked to small post #1, same thing.
d) If you hooked to small post #3, same thing.
So, the only thing that makes sense for your install the red wire in the diagram to big post #1 to get battery power all the time.(This is where Ford picks up power for the devices in the truck.) So, you can hook up your red wire to big post #1, go to the circuit breaker, and then to the relay.
So, your second point – The fuel pump relay (Separate from starter solenoid, used for gassers with EFI.)
You could use a spade terminal on the yellow wire from the diagram and plug/push into the correct connector on the fuel pump relay holder. (4 slots for the 4 connectors on the relay. (Could be 5)) Your truck does not have an electric fuel pump. So likely there is no relay there, if so, you can pull it. You would use the one slot that only gets power when the key is on. (Providing it is wired in on a diesel, never tried, but it likely is.) Then the relay will get power from the factory wiring when the key is turned to “on”. However, any wire that only gets power with the key on will work for the yellow activation wire.
Some other thoughts.
Yes, a circuit breaker is like a fuse. The yellow wire should be fused, by likely you will hook to the factory wiring and thus it is fused by default. But unlike a fuse a circuit breaker can heat up, trip, cool, reset over and over. A fuse gets hot, burns, and has to be replaced.
I would mount the pump lower on the passenger side wheel well and the relay on the passenger side fender well. Then most of your wiring is very short and to the point.
The relay also needs a ground wire, you can put the relay on the passenger fender wall. Then run a wire from the ground terminal on the relay, to a wire (May come with wires sticking out already.), put a o connector on the wire, and the screw you use to screw the relay to the firewall, just put the o part of the ground wire between the screw head and the relay. The screw will get ground from your truck fender.
Also check out this post, which turned into an electric fuel pump. This member tapped the injector pump solenoid for the yellow activation wire.
https://www.oilburners.net/threads/7-3-idi-wont-stay
So take some pics and share. Let us know how it goes!